1. Field of the Invention
The invention relates to optical diffusion, and in particular to an optical diffusion structure with an array of convex portions and concave portions alternatingly arranged.
2. Description of the Related Art
Light emitting diodes, rather than CCFLs, are applied in backlight modules due to low cost and simplified structure. To keep the light source uniform, an optical diffusion structure is used. For point light source or linear light sources, the diffusion structure is usually designed to diffuse light in one or two dimensions.
A conventional backlight module employs a diffusion plate which has a blurred structure, a grained structure or micro-lens array. The blurred structure causes intensity reduction. The grained structure has small diffusion angle and cannot easily control diffusion directions. The micro-lens array operates at high intensity and is able to control the diffusion direction. The methods of manufacturing micro-lens array comprise mechanical methods, thermal fusion methods, or other complex methods, wherein a laser dragging method is generally used.
A laser dragging method is shown in FIG. 1a. A laser beam B passes through a mask 5 and reaches a substrate 10. When the mask 5 moves in a direction L7, the laser beam etches the substrate 10 to form grooves 12 which constitute a micro-lens array. A sharp corner with curvature equal to zero is formed between two grooves 12. The factors for controlling laser dragging comprise dragging speed, laser power, and number of repeated operations, which affect the depth of the grooves 12. The profile of the micro-lens array, however, depends on the pattern of the mask. Referring to FIG. 1b, a pattern M3 with large openings and small openings is formed on a mask M30. The mask M30 is applied to the laser dragging method to form a plurality of first micro-lenses 202 (concave portions) and a second micro-lens (convex portions) 204 arranged alternatingly. The area of the openings determines the etching depth. An ellipse array pattern or circle array pattern can be applied.
FIG. 2a depicts an optical diffusion structure 200 manufactured by the mask M3 in FIG. 1b along with a diffusion plate 50. FIG. 2b depicts the intensity of light passing through the optical diffusion structure 200. The stripes in FIG. 2b represent the area where light is condensed. Number 30 represents LED array. FIG. 2c depicts a blurred structure 210 formed on the back of the optical diffusion structure 200 for enhanced light diffusion.